1. Field of the Invention
This invention relates to an improved process for preparing allylic pentavalent organophosphorus compounds. More particularly, this invention relates to a process of preparing allylic pentavalent organophosphorus diester compounds by reacting the corresponding allyl halide with an appropriate phosphite ester compound in the presence of a pentakis (phosphite) complex of a d.sup.8 transition metal.
2. Prior Art
Esters of vinyl phosphonic acid serve as useful reactants in a large number of reactions to form compounds which are useful in agriculture. The versatility of this intermediate material results from reactivity of the vinylic group toward nucleophilic compounds. By manipulations of this reactivity via reaction with nucleophilic compounds such as alcohols, thiols, amines, nitroalkanes, active methylene compounds and the like, a wide class of agricultural chemicals can be prepared. For example, esters of vinylphosphonic acid compounds can be reacted with phosgene or oxalyl chloride to prepare plant growth regulants as described in detail in German Offen No. 2,153,149 (1983). Similarly, such esters can be reacted with amines in accordance with the procedures of Bartlett, et al., Tet Letters 24:2937 (1973) to prepare phosphatase inhibitors.
Furthermore, esters of vinyl-phosphonic acid can be used as precursors in the preparation of compounds which can be used in fields other than agriculture. For example, these compounds can be used in the preparation of heat and light stabilizers for polymers as well as flame retardant or shrinkage retardant additives for polymers. Such uses are described in detail in U.S. Pat. Nos. 4,129,710, 2,784,206, and 2,784,169; German Offen No. 2,745,982; J. Appl. Polyn. Sci. 22: 2403-14 (1978); and the like.
Heretofore, some synthetic procedures for the preparation of vinylic phosphonate compounds have centered on reacting an appropriate vinylic halide with an appropriate trivalent phosphorous ester in accordance with the following reaction scheme: ##STR1## This procedure is known as the Michaeles - Arbuzov reaction. Examples of this procedure are described in "Organic Phosphorus Compounds" Vol. 7, pp. 1-486, John Wiley & Sons (1976). The Michaeles - Arbuzov reaction suffers from a number of well-known inherent defects. For example, except for the .alpha., .beta.-unsaturated systems, reactions involving the Michaeles - Arbuzov reaction have failed.
Similarly, reactions involving the use of transition metal salt catalysts have been used to prepare vinylic phosphonate compounds. For example, the transition metal salt catalyzed reaction of aromatic and vinylic halides with phosphites or similar trivalent phosphorus compounds to prepare the corresponding vinylic phosphonate compound is described in U.S. Pat. No. 3,493,639. This procedure also suffers from a number of defects. For example, severe reaction conditions have limited the application in industrial application.
As an alternative method, we have developed a process for the preparation of vinylic phosphonate ester compounds by isomerizing an allyl phosphonate ester into the desired vinyl phosphonate ester compound. This process is described in more detail in our copending U.S. patent application Ser. No. 627,144 entitled "BASE CATALYZED ISOMERIZATION OF ALLYL PHOSPHONATE DIESTERS TO VINYL PHOSPHONATE, DIESTERS", filed concurrently herewith and now U.S. Pat. No. 4,582,652. While this alternative process provides for excellent yields of the vinylic phosphonate ester compound it has not been totally acceptable primarily due to the lack of an acceptable commercial process for the manufacture of the allyl phosphonate ester precursor. Heretofore, pentavalent allyl phosphonate esters were prepared by either of two processes. One of these processes involves the direct reaction of an allylic halide compound with a trialkyl phosphite compound in the presence of a nickel halide catalyst at a high temperature. This process is described in detail in Japan Kokai No. 73 75, 528. The other process involves heating an allylic halide compound and a trialkyl phosphite compound in the presence of an alkyl amine in a sealed tube. This process is described in detail in Compt. Rend 259:2244 (1964). In both of these processes, conversion of the alkyl halide compound and trialkyl phosphite compound into the described product is low, and yields are not readily reproducible. These methods are obviosly not capable of commercial application for the preparation of allyl phosphonate compounds.
It is thus apparent that a need exists for an improved, practical and efficient method for the preparation of allylic phosphonate diester derivatives, which derivatives can be used as precursors in the preparation of vinyl phosphonate diester compounds.